In this protocol, we will evaluate patients without known immunocompromise, who have severe, persistent, or treatment-refractory viral infections caused by herpesviruses, adenoviruses, polyoma viruses, papillomaviruses, or other viral infections. We will investigate whether certain host or virologic factors predispose these individuals to severe disease. We will also determine the usefulness of various microbiologic tests (e.g., cultures, serology, molecular assays) for following the course of infection in these patients. The physicians in the Clinical Center will provide optimal therapy for these patients, as part of standard of care. Identification of virologic or host factors that predispose these patients to severe viral infections may have important implications for elucidating the pathogenesis of infection and for the development of novel therapies.